On Monday, the U.S. Geological Survey (USGS) issued an earthquake warning for a state east of the Rockies — for the first time ever. The warning was for Oklahoma, where the rate of earthquakes has increased by about 50 percent since last October. The sharp uptick in small quakes increased the likelihood of larger, more dangerous earthquakes — 5.0 and greater — in the future, the scientists warned.

Why is Oklahoma suddenly rivaling California for the most earthquakes per square mile? The researchers from USGS and the Oklahoma Geological Survey say that fracking activities may be contributing to the state’s new seismic reality.

“The recent earthquake rate changes are not due to typical, random fluctuations in natural seismicity rates,” the report stated.

While fracking itself has been linked to a handful of earthquakes, it is the injection of fracking wastewater deep into the earth that is believed to trigger most fracking-related tremors. The fluid increases underground pressure and acts as a lubricant on faults.

Oklahoma has been rocked by 183 earthquakes of magnitude 3.0 or greater between October 2013 and April 14, 2014. On average, this area sees just two such powerful earthquakes per year. And since 2009, when fracking took off in the state, Oklahoma has been shaken by 20 magnitude 4.0 to 4.8 quakes. On Nov. 5, 2011 a 5.6 earthquake — the largest ever recorded in the state — rocked the city of Prague, in central Oklahoma.

CREDIT: USGS

Last week scientists attending the Seismological Society of America annual meeting in Anchorage, Alaska called for more research into the relationship between fracking wastewater disposal and earthquake activity.

Gail Atkinson, an earth sciences professor at the University of Western Ontario, presented research at the conference highlighting the “significant and as-yet-unquantified risk” to the integrity of critical infrastructure, such as major dams and nuclear power plants posed by induced seismicity.

Part of the problem is that fault lines in the areas most affected by fracking operations are often poorly and incompletely mapped. Texas, Ohio, Colorado and Oklahoma, which have in recent years experienced unprecedented seismic activity, have never been made a priority like California and other states where quakes have long been a threat.

Infrastructure concerns were also brought up by USGS scientists as they warned Oklahoma that the state was at an increased risk for a big quake. Most buildings in the state are not built to withstand such a shaking. USGS, is in fact, just now beginning to gather and include data on induced seismic activity in its maps of seismic risk.

Cornell University geophysicist Katie Keranen, also released a new paper at the conference detailing how four high-volume wastewater injection wells in Oklahoma had triggered a wave of small earthquakes over 9 miles away.

“Our results, using seismology and hydrogeology, show a strong link between a small number of wells and earthquakes migrating up to 50 kilometers (31 miles) away,” said Keranen in a press release.

Even if the wastewater doesn’t travel that far, the pressure can radiate out inducing earthquakes in faults far removed from the injection site.

Last month, the Ohio Department of Natural Resources released strict new guidelines for monitoring seismic activity in the state. The rules require companies to install seismic monitors before beginning to drill within three miles of a known fault or in an area that has experienced seismic activity greater than 2.0 magnitude. If seismic monitors detect a quake of 1.0 or more, regulators will suspend fracking and investigate whether drilling is connected to the quake.

Ohio already has regulations against the disposal of fracking wastewater in certain counties where seismic activity has been a problem in the past.